Thermally conductive composite interface, cooled electronic assemblies employing the same, and methods of fabrication thereof

ABSTRACT

A composite interface and methods of fabrication are provided for coupling a cooling assembly to an electronic device. The interface includes a plurality of thermally conductive wires formed of a first material having a first thermal conductivity, and a thermal interface material at least partially surrounding the wires. The interface material, which thermally interfaces the cooling assembly to a surface to be cooled of the electronic device, is a second material having a second thermal conductivity, wherein the first thermal conductivity is greater than the second thermal conductivity. At least some wires reside partially over a first region of higher heat flux and extend partially over a second region of lower heat flux, wherein the first and second regions are different regions of the surface to be cooled. These wires function as thermal spreaders facilitating heat transfer from the surface to be cooled to the cooling assembly.

TECHNICAL FIELD

The present invention relates to heat transfer mechanisms, and moreparticularly, to heat transfer mechanisms and cooling assemblies forremoving heat generated by an electronic device. More particularly, thepresent invention relates to a thermally conductive composite interface,and methods of fabrication thereof, for interfacing a cooling assemblyto one or more heat-generating electronic devices.

BACKGROUND OF THE INVENTION

As is well known, operating electronic devices produce heat. This heatshould be removed from the devices in order to maintain device junctiontemperatures within desirable limits, with failure to remove the heatresulting in increased device temperatures, potentially leading tothermal runaway conditions. Several trends in the electronics industryhave combined to increase the importance of thermal management,including heat removal for electronic devices, including technologieswhere thermal management has traditionally been less of a concern, suchas CMOS. In particular, the need for faster and more densely packedcircuits has had a direct impact on the importance of thermalmanagement. First, power dissipation, and therefore heat production,increases as device operating frequencies increase. Second, increasedoperating frequencies may be possible at lower device junctiontemperatures. Finally, as more and more devices are packed onto a singlechip, power density (Watts/cm²) increases, resulting in the need toremove more power from a given size chip or module.

SUMMARY OF THE INVENTION

Cooling technologies utilize air or water to carry heat away from anelectronic device, and reject the heat to the ambient. Heat sinks withheat pipes or vapor chambers are commonly used air-cooling devices whilecold-plates are most predominant in water cooling approaches. With bothtypes of cooling assemblies, it is necessary to couple the coolingassembly to the electronic device. This coupling can result in a thermalinterface resistance between the cooling assembly and the electronicdevice. The interface coupling the cooling assembly to the electronicdevice should thus provide an effective thermal path for heat transferfrom the electronic device to the cooling assembly.

Additionally, semiconductor processing has progressed to the point wheremultiple logic units and their associated control and support circuitsare being located on a single integrated circuit chip. From a thermalviewpoint, this results in a device with a highly non-uniform heat fluxdistribution. A relatively high heat flux is generated in the processorcore region(s) and a relatively low heat flux is produced in thecontrol/support regions. For example, the core region heat flux can beas much as fifteen times greater than that of other regions. Thermalgrease conduction cooling schemes are not well suited to handle suchdisparate fluxes. They result in an equally disparate circuittemperature distribution, and more importantly, a much higher absolutejunction temperature within the high heat flux regions.

Provided herein in one aspect, is a thermally conductive compositeinterface for enhanced coupling of a cooling assembly to at least oneheat-generating electronic device. The thermally conductive compositeinterface includes a plurality of thermally conductive wires comprisinga first material having a first thermal conductivity, and a thermalinterface material at least partially surrounding the plurality ofthermally conductive wires when the thermally conductive compositeinterface is employed between the cooling assembly and a surface to becooled of the at least one heat-generating electronic device. Thethermal interface material includes a second material having a secondthermal conductivity, wherein the first thermal conductivity of thefirst material is greater than the second thermal conductivity of thesecond material. When the thermally conductive composite interface isemployed to couple the cooling assembly and the surface to be cooled, atleast some thermally conductive wires of the plurality of thermallyconductive wires reside partially over at least one first region ofhigher heat flux and extend partially over at least one second region oflower heat flux, wherein the at least one first region and the at leastone second regions are different regions of the surface to be cooled.When the thermally conductive composite interface is employed to couplethe cooling assembly and the surface to be cooled of the at least oneheat-generating electronic device, the at least some thermallyconductive wires function as thermal spreaders for facilitating heattransfer from the at least one heat-generating electronic device to thecooling assembly.

In another aspect, provided herein is a cooled electronic assembly. Thecooled electronic assembly includes a cooling assembly, at least oneheat-generating electronic device, and a thermally conductive compositeinterface. The at least one heat-generating electronic device has asurface to be cooled, which includes at least one region of higher heatflux and at least one region of lower heat flux. The thermallyconductive composite interface, which couples the cooling assembly andthe surface to be cooled, includes a plurality of thermally conductivewires and a thermal interface material. The plurality of thermallyconductive wires comprise a first material having a first thermalconductivity, and the thermal interface material comprises a secondmaterial having a second thermal conductivity, wherein the first thermalconductivity of the first material is greater than the second thermalconductivity of the second material. The thermal interface material atleast partially surrounds the plurality of thermally conductive wiresand thermally interfaces the cooling assembly to the surface to becooled. At least some thermally conductive wires of the plurality ofthermally conductive wires reside partially over the at least one firstregion of higher heat flux and extend partially over the at least onesecond region of lower heat flux to function as thermal spreadersbetween the surface to be cooled and the cooling assembly forfacilitating heat transfer from the at least one heat-generatingelectronic device to the cooling assembly.

In a further aspect, provided herein is a method of interfacing acooling assembly and a surface to be cooled of at least oneheat-generating electronic device. The method includes: providing aplurality of thermally conductive wires comprising a first materialhaving a first thermal conductivity; disposing the plurality ofthermally conductive wires between the cooling assembly and the surfaceto be cooled, with at least some thermally conductive wires of theplurality of thermally conductive wires residing partially over at leastone first region of higher heat flux of the surface to be cooled andextending partially over at least one second region of lower heat fluxof the surface to be cooled; and providing a thermal interface materialbetween the cooling assembly and the surface to be cooled at leastpartially surrounding the plurality of thermally conductive wires andthermally interfacing the cooling assembly to the surface to be cooled,wherein the at least some thermally conductive wires function as thermalspreaders between the surface to be cooled and the cooling assembly forfacilitating heat transfer from the at least one heat-generatingelectronic device to the cooling assembly.

Further, additional features and advantages are realized through thetechniques of the present invention. Other embodiments and aspects ofthe invention are described in detail herein and are considered a partof the claimed invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter which is regarded as the invention is particularlypointed out and distinctly claimed in the claims at the conclusion ofthe specification. The foregoing and other objects, features, andadvantages of the invention are apparent from the following detaileddescription taken in conjunction with the accompanying drawings inwhich:

FIG. 1 is a cross-sectional elevational view of one embodiment of aliquid-cooled electronic assembly, wherein a composite interface isemployed to couple the cooling assembly to the at least oneheat-generating electronic component, in accordance with an aspect ofthe present invention;

FIG. 2 is a cross-sectional elevational view of one embodiment of anair-cooled electronic assembly, wherein the cooling assembly is coupledto the at least one heat-generating electronic component employing acomposite interface, in accordance with an aspect of the presentinvention;

FIG. 3A is a plan view of one embodiment of a surface to be cooled of aheat-generating electronic device showing a first region of higher heatflux and a second region of lower heat flux to be interfaced forcooling, in accordance with an aspect of the present invention;

FIG. 3B is a plan view of the surface to be cooled of FIG. 3A with theaddition of multiple thermally conductive wires wire-bonded to thesurface to be cooled within the first region of higher heat flux andextending outward therefrom to the second region of lower heat flux, inaccordance with an aspect of the present invention;

FIG. 3C is a partial enlarged elevational view of one embodiment of onethermally conductive wire wire-bonded to the surface to be cooled, inaccordance with an aspect of the present invention;

FIG. 4A is an elevational view of a thermally conductive wire to bewire-bonded to a surface to be cooled during an interface method, inaccordance with an aspect of the present invention;

FIG. 4B depicts the structures of FIG. 4A showing the formation of adiffusion weld-bond between the wire and the surface to be cooled, inaccordance with an aspect of the present invention;

FIG. 4C depicts the structures of FIG. 4B showing the wire-bonding toolhead moved up the wire, after bending of the wire, and showing theapplication of an electronic flame-off (EFO) to the wire to cut the wireand thereby form the discrete thermally conductive wire attached to thesurface to be cooled, in accordance with an aspect of the presentinvention;

FIG. 5 is an isometric view of one embodiment of a heat-generatingelectronic device showing multiple thermally conductive wireswire-bonded to a first region of higher heat flux of the electronicdevice and extending over a second region of lower heat flux, andshowing wire-bonded studs at the corners of the electronic device toprovide a spacing between a cooling assembly (not shown) and the surfaceto be cooled when the thermally conductive composite interface isemployed to couple the cooling assembly and the surface to be cooled, inaccordance with an aspect of the present invention;

FIG. 6 is an isometric view of an alternate embodiment of aheat-generating electronic device showing multiple wire-bonded studs asstand-offs to provide a spacing between a cooling assembly (not shown)and the surface to be cooled, as well as to facilitate transfer of heatfrom a first region of higher heat flux of the surface to be cooled, inaccordance with an aspect of the present invention;

FIG. 7A is a partial cross-sectional elevational view of one embodimentof a cooled electronic assembly employing a thermally conductivecomposite interface to couple a cooling assembly and heat-generatingelectronic device, in accordance with an aspect of the presentinvention;

FIG. 7B is a partial cross-sectional elevational view of an alternateembodiment of a thermally conductive composite interface coupling acooling assembly and heat-generating electronic component, in accordancewith an aspect of the present invention;

FIG. 7C is a partial cross-sectional elevational view of anotherembodiment of a thermally conductive composite interface coupling acooling assembly and heat-generating electronic component, in accordancewith an aspect of the present invention;

FIG. 7D is a partial cross-sectional elevational view of a furtherembodiment of a thermally conductive composite interface coupling acooling assembly and heat-generating electronic component, in accordancewith an aspect of the present invention;

FIG. 7E is a partial cross-sectional elevational view of still anotherembodiment of a thermally conductive composite interface coupling acooling assembly and heat-generating electronic component, in accordancewith an aspect of the present invention;

FIG. 7F is a partial cross-sectional elevational view of an alternateembodiment of a thermally conductive composite interface coupling acooling assembly and heat-generating electronic component, in accordancewith an aspect of the present invention; and

FIG. 8 is a graph showing reduction in hot spot temperature achieved ata surface to be cooled of an electronic device for different wire-bonddensities of a composite interface and assuming two different regions ofheat flux, in accordance with an aspect of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Generally stated, disclosed herein is a thermally conductive compositeinterface for coupling a cooling assembly to one or more heat-generatingelectronic devices. The thermally conductive composite interfaceincludes a plurality of thermally conductive wires or pin fins, formedof a first material having a first thermal conductivity, and a thermalinterface material, which at least partially surrounds the plurality ofthermally conductive wires and thermally interfaces the cooling assemblyto a surface to be cooled of the one or more heat-generating electronicdevices when the thermally conductive composite interface is employedbetween the cooling assembly and the surface to be cooled. The thermalinterface material comprises a second material having a second thermalconductivity, wherein the first thermal conductivity of the firstmaterial is greater than the second thermal conductivity of the secondmaterial.

When the thermally conductive composite interface is employed to couplethe cooling assembly and the surface to be cooled, the at least somethermally conductive wires of the plurality of thermally conductivewires reside partially over at least one first region of higher heatflux and extend partially over at least one second region of lower heatflux, wherein the at least one first and second regions are differentregions of the surface to be cooled. In operation, the at least somethermally conductive wires function as thermal spreaders forfacilitating heat transfer from the surface to be cooled to the coolingassembly.

As used herein, “electronic device” comprises any heat-generatingcomponent of, for example, a computer system or other electronic systemrequiring cooling. The term includes one or more of an integratedcircuit chip, multiple integrated circuit chips, a single chip module ora multi-chip module, either with or without a thermal cap or thermalspreader. The “surface to be cooled” refers to a surface of theelectronic device itself, or to an exposed surface of a thermalspreader, passivation layer, thermal cap or other surface in contactwith the electronic device, and through which heat generated by theelectronic device is to be extracted.

Before describing embodiments of the thermally conductive compositeinterface in detail, two embodiments of a cooled electronic assembly(each employing a different cooling assembly, and a thermally conductivecomposite interface) are described with reference to FIGS. 1 & 2.

As noted initially, performance of computing devices continues todramatically improve. This phenomenon is primarily driven by thecontinuous reduction in transistor-length scales, which has in turnallowed greater functionality to be incorporated within the same orsmaller device footprints. Since most of the electrical energy consumedby these devices is released into the ambient environment in the form ofheat, the thermal management of electronic devices is a growingengineering challenge.

FIG. 1 depicts one embodiment of a cooled electronic assembly, generallydenoted 100, in accordance with an aspect of the present invention. Inthis embodiment, cooled electronic assembly 100 includes at least oneelectronic device 110 coupled to a cooling assembly 120 via an interface130. More particularly, compressive loading could be employed to forcecooling assembly 120 and at least one electronic device 110 together,with interface 130 sandwiched therebetween. In this example, coolingassembly is a liquid-cooled assembly, which includes a cold plate base122 cooled by liquid coolant (e.g., cooled water) passing through a coldplate housing 126 from an inlet 127 to an outlet 129 thereof. Cold platebase 122 has projecting therefrom multiple pins or fins 124 tofacilitate transfer of heat from cold plate base 122 to coolant flowingthrough manifold 126.

FIG. 2 depicts another example of a cooled electronic assembly,generally denoted 200, in accordance with an aspect of the presentinvention. Cooled electronic assembly 200 includes one or moreheat-generating electronic devices 210 coupled to a cooling assembly 220via an interface 230. In this example, cooling assembly 220 is anair-cooled heat sink having a thermally conductive base 222 with a vaporchamber 221 therein. Extending from thermally conductive base 222 are aplurality of pins or fins 224, which are air-cooled 225, either activelyor passively.

In both cooled electronic assembly embodiments of FIGS. 1 & 2, thecooling assembly is presented, by way of example, larger than the one ormore electronic devices to be cooled in order to facilitate transfer ofheat from the electronic device to the liquid coolant (in the example ofFIG. 1) or ambient air (in the example of FIG. 2). Typically, aircooling is a viable option when the average chip heat flux is below100-125 watts per square centimeter. For electronic device heat fluxesgreater than 125 watts per square centimeter, liquid cooling or anotheraggressive cooling technique is required. In the cooled electronicassemblies of FIGS. 1 & 2, an interface 130, 230 is used to thermallycouple (and if desired, structurally couple) the cooling assembly to theone or more electronic devices. This interface is conventionally formedof a thermal interface material such as thermal grease or athermo-setting epoxy or silicone. Such materials typically have thermalconductivities in the range of 0.1-4 W/m-K.

Air-cooled cooling assemblies, as well as liquid-cooled coolingassemblies, are normally designed to meet an average heat flux coolingrequirement. Traditionally, the average heat flux over the electronicdevice footprint has been a useful metric in determining the thermalchallenge, primarily because the maximum heat flux of the electronicdevice has conventionally been near its average value. However, withrecent advances in electronic circuit design, and particularly inmicroprocessor design, certain regions of the device may exhibit muchhigher heat fluxes than other regions, not only in steady stateoperation, but also when the device is switched on or off. These regionsof higher heat flux are referred to as “hot spots”, and they candissipate heat fluxes that are 2-3 times greater than the average heatflux for the electronic device. This spatial non-uniformity in deviceheat flux results in a corresponding spatial non-uniformity in thedevice temperature, and can lead to maximum hot spot temperatures thatare 10-20° C. higher than the device average temperature. In such cases,the cooling assembly performance is gated by this hot spot temperature.This phenomenon of hot spots is a local thermal issue, and is mosteffectively addressed locally. Thus, presented herein are variouscomposite interface structures and their methods of fabrication whichwhen employed significantly reduce hot spot temperatures by enhancingheat transfer from the high heat flux region(s) to the cooling assembly.

FIG. 3A depicts one example of a surface to be cooled 300 comprising asurface of or a surface attached to one or more electronic devices. Inthis example, the surface to be cooled includes a first region 310 ofhigher heat flux and a second region 320 of lower heat flux.Alternatively, multiple discrete regions 310 and/or regions 320 mayexist across the surface to be cooled 300. First region 310 of higherheat flux is assumed to have a significantly higher heat dissipationrate compared with the balance of the surface, and thus, is a hot spotregion.

FIG. 3B depicts the structure of FIG. 3A, with the addition of aplurality of thermally conductive wires 330 (or pin fins) bonded tofirst region 310 of higher heat flux. As shown, the thermally conductivewires 330 are bent to reside over first region 310 and extend partiallyover second region 320 of lower heat flux. These wires thus function asthermal spreaders for facilitating heat transfer from the higher heatflux region of the surface to be cooled to the cooling assembly whenemployed as part of a composite interface between the surface to becooled and the cooling assembly.

FIG. 3C illustrates one example of a thermally conductive wire 330′which (as one example) is wire-bonded 332 to the surface to be cooled300, such as the back surface of an integrated circuit chip. Currentwire-bonding interconnect technology may be used to create 0.025-0.1 mmdiameter wires 330′ wire-bonded to the surface to be cooled within thehot spot region. By way of example, the thermally conductive wire 330′comprises a metal such as gold, copper or aluminum and has a length todiameter aspect ratio of greater than 40:1. Copper wire has a thermalconductivity of 400 W/m-K, which is approximately 100 times the thermalconductivity of today's thermal interface material, i.e., thermalgrease, which has a thermal conductivity of 3-4 W/m-K. The array ofthermally conductive wires is effective in reducing the temperature inthe higher heat flux region of the surface to be cooled by twomechanisms, namely, by increasing the thermal conductivity of thethermal interface in the region of higher heat flux, and by radiallyspreading heat from the higher heat flux region to the coolersurrounding regions of lower heat flux.

FIGS. 4A-4C illustrate one method of fabricating the thermallyconductive wires, in accordance with an aspect of the present invention,using thermosonic ball-bonding techniques.

FIG. 4A depicts the beginning of the manufacturing process, displayingthe various elements needed for the process, including a surface to becooled 300 of one or more electronic devices, and wire 400 that is to beformed into a plurality of thermally conductive wires or pins. Wire 400includes a ball tip 405 and the tool head that incorporates thewire-clamping mechanism includes a capillary passage 410 for the wire.Appropriate metallization (such as chrome-copper or chrome-copper-gold)is assumed to reside on the surface to be cooled 300. In FIG. 4B, theclamping mechanism of tool head 412 is shown in clamped position holdingwire 400.

FIG. 4B illustrates the tool head of FIG. 4A after the ball tip of wire400 has been brought into physical contact with the surface to becooled. Using a controlled downward bond force in combination withultrasonic activation, a physical environment is created that isconducive to plastic deformation and intermolecular diffusion betweenwire 400 and the metalized surface to be cooled. A diffusion weld-bond415 results under these conditions, whereby the plastic deformation atmicroscopic length scales causes the metal to flow in slip and shearplanes across each part of the wire-surface interface, thus forming ametallurgical diffusion bond.

After the bond is formed, the tool head is unclamped, and moved to adifferent position along the length of wire 400, during which bends areformed in the wire as shown in FIG. 4C. An electronic flame-off (EFO)operation, which is a process known in the art for cutting a wire, isthen employed to sever wire 400 at the second bend in the wire, whichalso creates a new ball tip (not shown) to allow re-initiation of theprocess. (Alternatively, a notch and cut operation could be employed toserver wire 400.) Numerous repetitions of the process can be performedto produce a wire array such as depicted in FIG. 3B. Those skilled inthe art should note from this description that any desired wirearrangement can be accommodated. Further, although initially describedas being attached to the surface to be cooled, those skilled in the artwill note from this description that the plurality of thermallyconductive wires could additionally or alternatively be wire-bonded to asurface of the cooling assembly.

FIG. 5 depicts an enlarged example of an electronic device 500, such asan integrated circuit chip, having a first region 510 of higher heatflux and multiple second regions 520 of lower heat flux. A plurality ofwire-bonded wires 530 are attached to first region 510 of higher heatflux with the wires extending from the first region to over the secondregions 520 of lower heat flux. As explained further below, theplurality of thermally conductive wires 530 are suspended at leastpartially within a thermal interface material when employed in thecomposite interface. In this example, stand-offs 540 are also providednear the corners of the electronic device to ensure reliable positioningof the cooling assembly relative to the electronic device. In oneexample, these stand-offs are four bumps formed at the corners of theelectronic device before the thermal interface material has been added.The bumps can be created by following a similar process to thatdescribed above in connection with FIGS. 4A-4C, but with cut-offoccurring close to where the ball joint is made, at a very shortspecific length of wire. These bump structures can be used in the hotspot region as well, as illustrated in FIG. 6, wherein a plurality ofwire-bonded bumps 600 are secured to first region 510 of higher heatflux. Additionally, wire-bonded bumps 600 could be interleaved (notshown) with the plurality of thermally conductive wires 530 (FIG. 5) inany desired pattern.

FIGS. 7A-7F are partial cross-sectional elevational views of variousembodiments of a thermally conductive composite interface coupling acooling assembly 730 and a heat-generating electronic device 700. Asshown, heat-generating electronic device 700 includes at least tworegions, that is, a first region 710 of higher heat flux, and a secondregion 720 of lower heat flux. In each embodiment, a single wire 740 isshown at least partially suspended within a thermal interface material750, such as a thermally conductive grease. Cooling assembly 730 may,e.g., comprise a cooling assembly such as described above in connectionwith FIGS. 1 & 2. Alternatively, cooling assembly 730 could simplycomprise a metal lid, such as a copper cover, over the electronic device700.

In the embodiment of FIG. 7A, a wire 740 (e.g., 1-2 mil diameter) iswire-bonded at a first end to the surface to be cooled within firstregion 710 of the electronic device 700. A second end of wire 740 issuspended within the thermally conductive grease 750 and extends oversecond region 720 of lower heat flux.

FIG. 7B depicts an alternate configuration wherein thermally conductivewire 740 is again (e.g., a 1-2 mil diameter wire) wire-bonded to thesurface to be cooled within first region 710 of higher heat flux. Inthis example, wire 740 partially contacts cooling assembly 730 andextends over second region 720 of lower heat flux.

FIG. 7C depicts another embodiment wherein thermally conductive wire 740is surrounded by thermally conductive material 750 and includes a firstend which resides over first region 710 of higher heat flux and a secondend which resides over second region 720 of lower heat flux. In thisembodiment, no wire-bonding of wire 740 to either the surface to becooled or the cooling assembly is employed. By way of example, thermallyconductive wire 740 could comprise gold, copper, aluminum or graphite.

FIG. 7D depicts an embodiment wherein thermally conductive wire 740 iswire-bonded to cooling assembly 730 aligned over first region 710 ofhigher heat flux of electronic device 700. The free end of thermallyconductive wire 740 is suspended within thermal interface material 750and extends over second region 720 of electronic device 700.

FIG. 7E depicts a variation on the embodiment of FIG. 7D, whereinthermally conductive wire 740 at least partially physically contactselectronic device 700 to facilitate transfer and spreading of heat fromfirst region 710 of higher heat flux into the composite interface andhence to cooling assembly 730.

FIG. 7F depicts a further variation on the composite interface, whereinthermally conductive wire 740 is attached (for example, wire-bonded) tothe surface to be cooled and attached (for example, soldered) to coolingassembly 730. In the example shown, wire 740 is joined to the electronicdevice 700 in first region 710 of higher heat flux, and extends to aposition over second region 720 of lower heat flux where wire 740attaches to cooling assembly 730. As with the other embodiments, wire740 is, e.g., a 1-2 mil diameter wire that is at least partiallysurrounded by thermal interface material 750.

Thermal analysis has been performed to evaluate the impact of athermally conductive composite interface as described herein on maximumhot spot temperature of an integrated circuit chip. This analysis wascarried out on a 10 mm by 10 mm integrated circuit chip that was 0.75 mmthick, and made of silicon (120 W/m-K), attached to a liquid-cooled coldplate via 0.076 mm (3 mils) thick thermal interface material, e.g.,thermal grease (3.8 W/m-K). By way of example, 89% of the chipdissipated heat at a flux of 132 watts per square centimeter, while ahot spot was set to a heat flux of 250-350 watts per square centimeter.Without a plurality of thermally conductive wires, a maximum junctiontemperature of 110° C. was noted for a case with a 350 W/cm² hot spotheat flux, while with a plurality of thermally conductive wires disposedas illustrated in FIG. 3B, a maximum junction temperature of 99° C. wasobtained. More specifically, in one example, the thermally conductivewire was assumed to comprise copper wire of 1 mil diameter and 2 mm inlength. A quantity of 240 such wires was employed in the analysis.

FIG. 8 is a graph of the reduction in the hot spot integrated circuitchip junction temperature for several different wire-bond densities, andfor two hot spot heat fluxes of 250 and 350 watts per square centimeter,respectively. The graph illustrates that adding more wires to the hotspot region results in an increased reduction in the hot spottemperature. Further, the impact of the thermally conductive compositeinterface disclosed herein is greater as the magnitude of the hot spotheat flux increases. The baseline hot spot temperature was 95° C.maximum for a 250 watts/cm² hot spot and 110° C. maximum for a 350 W/cm²hot spot.

Although preferred embodiments have been depicted and described indetail herein, it will be apparent to those skilled in the relevant artthat various modifications, additions, substitutions and the like can bemade without departing from the spirit of the invention and these aretherefore considered to be within the scope of the invention as definedin the following claims.

1. A thermally conductive composite interface for coupling a coolingassembly to at least one heat-generating electronic device, thethermally conductive composite interface comprising: a plurality ofthermally conductive wires comprising a first material having a firstthermal conductivity; a thermal interface material at least partiallysurrounding the plurality of thermally conductive wires and thermallyinterfacing the cooling assembly to a surface to be cooled of at leastone heat-generating electronic device when the thermally conductivecomposite interface is employed between the cooling assembly and thesurface to be cooled, the thermal interface material comprising a secondmaterial having a second thermal conductivity, wherein the first thermalconductivity of the first material is greater than the second thermalconductivity of the second material; and wherein when the thermallyconductive composite interface is employed to couple the coolingassembly and the surface to be cooled, at least some thermallyconductive wires of the plurality of thermally conductive wires residepartially over at least one first region of higher heat flux and extendpartially over at least one second region of lower heat flux, the atleast one first region and the at least one second region comprisingdifferent regions of the surface to be cooled of the at least oneheat-generating electronic device, and wherein the at least somethermally conductive wires function as thermal spreaders forfacilitating heat transfer from the surface to be cooled of the at leastone heat-generating electronic device to the cooling assembly.
 2. Thethermally conductive composite interface of claim 1, wherein the atleast some thermally conductive wires are at least partially suspendedwithin the thermal interface material when the thermally conductivecomposite interface is employed between the cooling assembly and thesurface to be cooled of the at least one heat-generating electronicdevice.
 3. The thermally conductive composite interface of claim 1,wherein the at least some thermally conductive wires of the plurality ofthermally conductive wires are wire-bonded to at least one of a surfaceof the cooling assembly or the surface to be cooled of the at least oneheat-generating electronic device when the thermally conductivecomposite interface is employed to couple the cooling assembly and thesurface to be cooled.
 4. The thermally conductive composite interface ofclaim 3, wherein the at least some thermally conductive wires are eachseparately wire-bonded at a first end to the surface to be cooled of theat least one heat-generating electronic device in the at least one firstregion of higher heat flux.
 5. The thermally conductive compositeinterface of claim 4, wherein a second end of each of the at least somethermally conductive wires is disposed over the at least one secondregion of lower heat flux and is one of suspended within the thermalinterface material, partially contacting of the cooling assembly, orattached to a surface of the cooling assembly when the thermallyconductive composite interface is employed to couple the coolingassembly and the surface to be cooled of the at least oneheat-generating electronic device.
 6. The thermally conductive compositeinterface of claim 1, wherein the first material of the plurality ofthermally conductive wires comprises at least one of gold, copper,aluminum or graphite, and wherein the second material of the thermalinterface material comprises one of a thermally conductive grease, anepoxy, an elastomer material or a liquid metal.
 7. The thermallyconductive composite interface of claim 1, wherein the first thermalconductivity of the first material is greater than ten times the secondthermal conductivity of the second material, and wherein the at leastone heat-generating electronic device comprises at least one of anintegrated circuit chip, multiple integrated circuit chips, a singlechip module or a multi-chip module.
 8. The thermally conductivecomposite interface of claim 1, further comprising multiple wire-bondedstuds attached to at least one of a surface of the cooling assembly orthe surface to be cooled of the at least one heat-generating electronicdevice when the thermally conductive composite interface is employed tocouple the cooling assembly and the surface to be cooled, and whereineach wire-bonded stud is at least one of: configured as a stand-off toprovide a spacing between the cooling assembly and the surface to becooled when the thermally conductive composite interface is employed tocouple the cooling assembly and the surface to be cooled; and alignedover the at least one first region of higher heat flux of the surface tobe cooled of the at least one heat-generating electronic device tofacilitate transfer of heat therefrom.
 9. A cooled electronic assemblycomprising: a cooling assembly; at least one heat-generating electronicdevice including a surface to be cooled, wherein the surface to becooled includes at least one first region of higher heat flux and atleast one second region of lower heat flux; and a thermally conductivecomposite interface coupling the cooling assembly and the surface to becooled, the thermally conductive composite interface comprising: aplurality of thermally conductive wires comprising a first materialhaving a first thermal conductivity; a thermal interface material atleast partially surrounding the plurality of thermally conductive wiresand thermally interfacing the cooling assembly to the surface to becooled of the at least one heat-generating electronic device, thethermal interface material comprising a second material having a secondthermal conductivity, wherein the first thermal conductivity of thefirst material is greater than the second thermal conductivity of thesecond material; and wherein at least some thermally conductive wires ofthe plurality of thermally conductive wires reside partially over the atleast one first region of higher heat flux and extend partially over theat least one second region of lower heat flux to function as thermalspreaders between the surface to be cooled and the cooling assembly forfacilitating heat transfer from the at least one heat-generatingelectronic device to the cooling assembly.
 10. The cooled electronicassembly of claim 9, wherein the at least some thermally conductivewires are at least partially suspended within the thermal interfacematerial.
 11. The cooled electronic assembly of claim 9, wherein the atleast some thermally conductive wires of the plurality of thermallyconductive wires are each separately wire-bonded at a first end to atleast one of a surface of the cooling assembly or the surface to becooled over the at least one first region of higher heat flux.
 12. Thecooled electronic assembly of claim 11, wherein each of the at leastsome thermally conductive wires is separately wire-bonded at the firstend to the surface to be cooled of the at least one heat-generatingelectronic device in the at least one first region of higher heat flux,and a second end of each of the at least some thermally conductive wiresis disposed over the at least one second region of lower heat flux andis one of suspended within the thermal interface material, partiallycontacting of the cooling assembly, or attached to the surface of thecooling assembly.
 13. The cooled electronic assembly of claim 9, whereinthe first material of the plurality of thermally conductive wirescomprises at least one of gold, copper, aluminum or graphite, andwherein the second material of the thermal interface material comprisesone of a thermally conductive grease, an epoxy, an elastomer material ora liquid metal.
 14. The cooled electronic assembly of claim 9, whereinthe first thermal conductivity of the first material is greater than tentimes the second thermal conductivity of the second material, andwherein the at least one heat-generating electronic device comprises atleast one of an integrated circuit chip, multiple integrated circuitchips, a single chip module or a multi-chip module.
 15. The cooledelectronic assembly of claim 9, further comprising multiple wire-bondedstuds attached to at least one of a surface of the cooling assembly orthe surface to be cooled of the at least one heat-generating electronicdevice, and wherein each wire-bonded stud is at least one of: configuredas a stand-off to provide a spacing between the cooling assembly and thesurface to be cooled; and aligned over the at least one first region ofhigher heat flux of the surface to be cooled to facilitate transfer ofheat therefrom.
 16. A method of interfacing a cooling assembly and asurface to be cooled of at least one heat-generating electronic device,the method comprising: providing a plurality of thermally conductivewires comprising a first material having a first thermal conductivity;disposing the plurality of thermally conductive wires between thecooling assembly and the surface to be cooled, with at least somethermally conductive wires of the plurality of thermally conductivewires each residing partially over at least one first region of higherheat flux of the surface to be cooled and extending partially over atleast one second region of lower heat flux of the surface to be cooled;and providing a thermal interface material between the cooling assemblyand the surface to be cooled at least partially surrounding theplurality of thermally conductive wires and thermally interfacing thecooling assembly to the surface to be cooled, wherein the at least somethermally conductive wires function as thermal spreaders between thesurface to be cooled and the cooling assembly for facilitating heattransfer from the at least one heat-generating electronic device to thecooling assembly.
 17. The method of claim 16, wherein the disposingcomprises wire-bonding the at least some thermally conductive wires ofthe plurality of thermally conductive wires to at least one of a surfaceof the cooling assembly or the surface to be cooled of the at least oneheat-generating electronic device.
 18. The method of claim 17, whereinthe wire-bonding of the at least some thermally conductive wirescomprises separately wire-bonding a first end of each thermallyconductive wire of the at least some thermally conductive wires to thesurface to be cooled within the at least one first region of higher heatflux.
 19. The method of claim 18, wherein the disposing furthercomprises positioning a second end of each of the at least somethermally conductive wires over the at least one second region of lowerheat flux to be one of suspended within the thermal interface material,partially contacting of the cooling assembly, or attached to a surfaceof the cooling assembly.
 20. The method of claim 16, further comprisingproviding multiple wire-bonded studs attached to at least one of asurface of the cooling assembly or the surface to be cooled of the atleast one heat-generating electronic device, wherein each wire-bondedstud is at least one of: configured as a stand-off to provide a spacingbetween the cooling assembly and the surface to be cooled; and alignedover the at least one first region of higher heat flux of the surface tobe cooled to facilitate transfer of heat therefrom.